Device for the display of local disorientations in single crystals

ABSTRACT

The device comprises a monochromatic X-radiation source from which a beam of incident X-rays is directed onto a single crystal, a system for detecting the intensity of the diffracted emergent beam by means of a stationary screen with a selecting slit, a movable screen having a variable-aperture analyzing slit and a moving photographic film, the X-ray source being &#39;&#39;&#39;&#39;seen&#39;&#39;&#39;&#39; from the single crystal at a substantial solid angle of the same order of magnitude as the disorientations to be recorded on the film. The single crystal is displaced by means of a goniometer mounted on a carriage which is driven in translational motion substantially at right angles to the direction of the incident Xray beam. Single-crystal samples several centimeters in thickness and of widely varying chemical composition can be analyzed by means of the device without any attendant danger of destruction.

United States Patent [191 Pluchery et al.

\ [451 Dec. 17,1974

[ DEVICE FOR THE DISPLAY OF LOCAL DISORIENTATIONS IN SINGLE CRYSTALS [75] Inventors: Max Pluchery, Grenoble; Claude Roughon, Fontaine, both of France [73] Assignee: Commissariat A LEnergie Atomique, Paris, France 22 Filed: Aug. 29, 1973 [21] App]. No.: 392,439

Related US. Application Data [63] Continuation of Ser. No. 222,634, Feb. 1, i972,

abandoned.

[30] Foreign Application Priority Data Feb, 3, 1971 France 71.03560 [52] US. Cl. 250/272, 250/275 [5 1] Int. Cl. GOln 23/22 [58] Field of Search 250/275, 274, 273, 272

[56] References Cited UNITED STATES PATENTS 2,079,900 5/1937 Cohn 250/275 OTHER PUBLICATIONS New X-Ray Topographic Technique for Detection of Small Defects in Highly Perfect Crystals, Chikawa,

Journal of Applied Phys, 4/70 p. 1922-1925.

Primary Examiner-James W. Lawrence Assistant Examiner-C. E. Church Attorney, Agent, or Firm-Cameron, Kerkam, Sutton, Stowell & Stowell [57] ABSTRACT The device comprises a monochromatic X-radiation source from which a beam of incident X-rays is directed onto a single crystal, a system for detecting the intensity of the diffracted emergent beam by means of a stationary screen with a selecting slit, a movable screen having a variable-aperture analyzing slit and a moving photographic film, the X-ray source being seen from the single crystal at a substantial solid angle of the same order of magnitude as the disorientations to be recorded on the film.

The single crystal is displaced by means of a goniometer mounted on a carriage which is driven in translational motion substantially at right angles to the direction of the incident X-ray beam.

Single-crystal samples several centimeters in thickness and of widely varying chemical composition can be analyzed by means of the device without any attendant danger of destruction.

3 Claims, 4 Drawing Figures PATENTED BEE] 7 74 SHEET 1 0F 2 FIGA FIG}

DEVICE FOR THE DISPLAY OF LOCAL DISORIENTATIONS IN SINGLE CRYSTALS This is a continuation, of application Ser. No. 222,634, filed Feb. 1, 1972 now abandoned.

It is known that, when a beam of X-rays falls on a crystal, part of the incident energy can be diffracted from the different lattice planes of said crystal.

The numerous methods of X-ray diffraction employed for the purpose of characterizing disorientations in single crystals belong to three general types based on wholly distinct principles and each having their particular field of application:

the first method or so-called Laue method is applicable to substantial disorientations (/2 to the second method involving the occurrence of focused Laue spots, or Guinier-Tennevin method, is applicable to disorientations of medium value (namely a few minutes),

the third or so-called Lang method and other methods derived from the dynamic theory of X-ray diffraction are applicable to very small disorientations (namely a few seconds).

The second category covers a large number of these techniques; in point. of fact, the application of the method referred-to becomes impossible as soon as the thickness of the sample exceeds one millimeter.

The present method, which is based on an entirely different principle, overcomes this disadvantage, particularly in the case of crystals formed of light elements in which thicknesses of several centimeters can be ex amined without destruction of the sample.

This invention relates to a device for thedisplay of local disorientations in single crystals, of the type in which use is made of a monochromatic X-radiation source, a beam of incident X-rays directed onto the single crystal, a system for detecting the intensity of the diffracted emergent X-ray beam, means for displacing the single crystal, characterized in that said X-ray source is seen from the single crystal at a substantial solid angle of the order of magnitude of the disorientations to be displayed.

It is therefore apparent that, in contrast to the devices involving the use of the Lang method which comprise a stopping-down slit having a very small transverse dimension and placed in front of. the X-ray source, the invention proposes the use of a source of substantial width which consequently deliveres a more intense incident beam and is more suitable than the methods of the prior art for the detection of disorientations of substantial amplitude and extent.

In accordance with one particular embodiment, the means for displacing the single crystal comprise a goniometric clamp on which the crystal is placed and which is capable of pivoting about its own axis, a carriage on which said clamp is mounted and adapted to be driven in translational motion substantially at right angles to the direction of the incident X-ray beam.

in a first alternative embodiment, the system for detecting the intensity of the diffracted emergent beam comprises a stationary screen having a selecting slit, placed downstream of the crystal and permitting said diffracted beam to pass therethrough and a stationary photographic film located at a short distance behind the selecting slit.

in a second alternative embodiment, the system for detecting the intensity of the diffracted emergent beam comprises a stationary screen having a selecting slit,

placed downstream of the crystal and permitting said diffracted beam to pass therethrough, and a moving photographic film displaceable in translational motion parallel to the direction of motion of said single crystal, said film being placed at a substantial distance behind said selecting slit, and an analyzing slit with adjustable position and aperture which is placed upstream of said moving film.

Further characteristic features of the invention will become apparent from the following description, reference being made to the accompanying drawings which show one non-limitative example of construction of said device, and in which:

FIG. 1 is a general arrangement diagram of the device according to the invention;

FIG. 2 is a synoptic view of one embodiment of said device;

FlGS. 3 and 4 are views respectively in side elevation and front elevation, of the screen which is provided with a slit and employed in the device of FIG. 2 for topographic photography of local disorientations of a crystal.

The source of monochromatic X-radiation is shown at 10 in FIG. 1 and is constituted by an anticathode tube of molybdenum, silver or tungsten. There is placed in front of this source a crystal sample 11 which is assumed to be in the position of reflection. Beyond this sample is placed a screen 12 with a selecting slit 13; this slit is designed so as to permit the passage of the beam which is diffracted from this lattice planes of a small predetermined region of the crystal 11.

If the sample were a perfect single crystal in the region under analysis, a motionless photographic film 14 located beyond the slit 13 would be exposed at the level of the point Mo along a straight-line segment at right angles to the plane of the figure.

On the contrary, when said region comprises a crystal disorientation which is not contained within the reflecting plane chosen, there is a displacement of the point of impact on the film 14 from the point M0 to the point It will now be assumed that the crystal sample is dis placed in translational motion in the direction T parallel to the screen 12 in order to scan'eith'er the complete sample or only part of this latter. There is then collected on the stationary photographic film a rectilineal image band, the width of which indicates the overall disorientation of the entire zone which is being scanned.

Let it now be assumed that the photographic film 14 is displaced in a movement of translation T parallel to the movement T preferably in the opposite direction, and that an analyzing slit 15 formed on a stationary screen 16 located upstream of the film is placed in position prior to recording to the image. There will then be formed on this film a topographic image of all the small regions which have a certain disorientation, the effect of any disorientation being to produce a weaker image on the film; the mean value and variations of this disorientation depend on the position and width which are given to the analyzing slit.

There will now be described with reference to FIGS. 2 to 4 a general arrangement of a device according to the invention which is based on the principle explained in the foregoing, and the practical conditions to be observed at the time of utilization of this device will become apparent from the passages relating to its operation.

As shown in FIG. 2, the source is provided on the monochromatic beam exit side with a tube 17 for protection against diffused radiation. The device proper is mounted on a rigid base-plate 18 of rectangular shape which has an oblique elongated extension plate 19 located in the same plane and having a length of approximately l meter. The different elements of the device can be inserted into the base-plate in holes and grooves which are formed in this latter.

The sample 11 is fixed on a goniometric clamp 20; said clamp can be driven in a movement of rotation in both directions (as shown by the arrow f) about its own axis located at right angles to the plane of the figure in order to place the crystal in the position of reflection; if necessary, said clamp can be endowed with a second movement of rotation or pivotal movement about an axis which is located in the plane of the figure and substantially at right angles to the direction of the X- radiation; this movement may prove necessary in order to provide optimum vertical adjustment of the position of the crystal.

The goniometric clamp 20 is mounted on a carriage 22 which is supported and guided by means of a dovetail coupling; the female portion of this dovetail coupling can be the section of a guiding groove formed in the base-plate 18 at right angles to the incident radiation; the carriage 22 is driven in translational motion by means of a reduction-gear motor 23.

The screen 12 with selecting slot 13 is removable and capable of displacement in its plane in such manner as to adjust the position of the slit by means of a micrometer screw 24.

The operation which consists in putting the crystal in the position of reflection accordingly takes place as follows:

An X-ray detector 25, preferably of the scintillation counter type, is placed temporarily on the base-plate 18 in the reflection location; said counter is connected electrically by means of the wires 21 to a summaryanalysis system (not shown) which indicates the presence of X-rays by means of a sound signal. The slit screen 12 is removed and the X-ray beam which emerges from the tube 17 is limited by means of a diaphragm 26 in order to prevent saturation of the detector. The-orientation of the goniometric clamp is ad justed coarsely to within i 2 until the crystal sample is in the reflection position as indicated by the sound signal; the diaphragm 26 is withdrawn; the slit" screen 13 is replaced and its position is adjusted. The detector is then withdrawn.

It is now possible to proceed with the detection of local disorientations of the crystal. As a first approximation, there is placed on the base-plate 18 at 27, a

sample crystal and can be driven in translational motion by means of a second reduction-gear motor 28. (If this film were stationary, it would simply record an image similar to that of the film-holder 27 but enlarged and permitting the display of smaller disorientations).

Positioning and adjustment of the analyzing slit i must be carried out with a sufficient degree of accuracy photographic film-holder which serves to obtain the to obtain a significant topographic image. As shown in FIGS. 3 and 4, the screen 16 which carries said slit has the shape of a disc, the bottom portion of which carries a set of spur teeth 29 over approximately one-quarter of the circumference; a pinion 30 having spur teeth is disposed in meshing engagement with the teeth of the screen and is operated manually by means of a knurled knob 31, thus permitting adjustment of the transverse inclination of the slit 15.

As indicated in FIG. 2, this slit can be brought to its working position by translational motion of the disc 16 about its own axis by means of the screw 33.

Finally, the slit is adjustable for width (as shown in FIGS. 3 and 4) by means of a system comprising a cylindrical plug 32 (similar to the plug of a stop-cock) which extends along a diameter of the disc 16 and can be pivoted by means of the screw 34; FIG. 3 shows that, at the time of arrival of R X-radiation, the width of the X-ray beam which passes through the slit depends on the longitudinal inclination given to the cylindrical plug. This width of slit must be equal at a maximum to the thickness of the beam diffracted from a perfect crystal; in fact, in any small scanned region of a crystal undergoing displacement, it is necessary to prevent the formation of another image on the film by a portion of the beam which corresponds to a perfect crystal; if this were to occur, it would be difficult to detect with accuracy any widening of the beam which results from a disorientation. In other words, if the intensity of the beam is recorded beforehand in the case of a perfect crystal, a reduction of intensity (more or less intense exposure of the film) corresponds to widening of the beam as a result of a disorientation. The necessary fine adjustment of the slit can be achieved by means of the cylindrical-plug system.

The reduction-gear motors 23 and 28 are chosen and adjusted in such manner that the speeds of translational motion of the film, of the film-holder l4 and of the sample 11 are in the same ratio as the distances between tube 17 and film l4 and between tube 17 and sample 11; it should be noted in addition that, in the case of the dimensions chosen and all other conditions being equal, the rate of scanning of the single crystal must be 10 to 20 times lower in the case of the topo graphic image than in the case of the general image.

If these directions are followed the image recorded on the moving film is free from distortion and reproduces the sample with an enlargement equal to the ratio of distances given above.

A device according to the invention makes it possible to work on single crystals of very variable chemical nature, the maximum thickness of which can extend from 1 to 50 mm approximately. The disorientations displayed (beneath boundaries or distortions of either thermal or mechanical origin) are within the range of l to l.

When a given crystal is examined a number of times in the monochromaticlight of different reflections, the regions which are either disoriented or perturbed can be localized in three dimensions. The procedure is applicable to single crystals having a thickness e and an absorption coefficient a for the K a radiation of tungsten, such that:

A few examples which confirm the performances of the device according to the invention are given in the following table:

Single crystal Anticathode Maximum thickness Be M0 or Ag 50 A1 0; W 40 Si W 40 SiO W- 40 Be 0 Ag Ga P W 6 Cd Te W l The maximum thickness can depend on the anticathode which is employed; thus, if the anticathode is silver, this thickness is reduced to 4 mm in the case of silicon and to 5 mm in the case of SiO emergent X-ray beam from the crystal, means for displacing the single crystal, said X-ray source being seen from the single crystal at a substantial solid angle on, the order of l' to 1 and said beam of incident X-ray being substantially divergent with an aperture angle of from 1' to 1, said means for displacing the single crystal including a rotatable goniometric clamp supporting the crystal, a carriage supporting said clamp, means for moving said clamp substantially at right angles to the direction of the incident X-ray beam, said means for detecting the intensity of the diffracted emergent beam including a stationary screen having a selecting slit downstream of the crystal for passage of said diffracted beam.

2. A device according to claim 1, wherein the system for detecting the intensity of the diffracted emergent beam comprises a stationary screen, a selecting slit in said screen downstream of the crystal, said diffracted beam passing through said slit. and including a moving photographic film displaceable in translational motion parallel to the direction of movement of said single crystal, said film being a substantial distance behind said selecting slit, an adjustable position analyzing slit and an adjustable aperture for said analyzing slit upstream of said moving film.

3. A device according to claim 1, wherein the system for detecting the intensity of the diffracted emergent beam comprises a stationary screen, a selecting slit in said screen, downstream of the crystal, said diffracted beam, passing through said slit and including a stationary photographic film a short distance behind said selecting slit. 

1. A device for the display of local disorientations in single crystals comprising a monochromatic X-radiation source, means for directing a beam of incident X-rays from said source onto the single crystal, means for detecting the intensity of the diffraction emergent X-ray beam from the crystal, means for displacing the single crystal, said X-ray source being seen from the single crystal at a substantial solid angle on the order of 1'' to 1* and said beam of incident X-ray being substantially divergent with an aperture angle of from 1'' to 1*, said means for displacing the single crystal including a rotatable goniometric clamp supporting the crystal, a carriage supporting said clamp, means for moving said clamp substantially at right angles to the direction of the incident X-ray beam, said means for detecting the intensity of the diffracted emergent beam including a stationary screen having a selecting slit downstream of the crystal for passage of said diffracted beam.
 2. A device according to claim 1, wherein the system for detecting the intensity of the diffracted emergent beam comprises a stationary screen, a selecting slit in said screen downstream of the crystal, said diffracted beam passing through said slit, and including a moving photographic film displaceable in translational motion parallel to the direction of movement of said single crystal, said film being a substantial distance behind said selecting slit, an adjustable position analyzing slit and an adjustable aperture for said analyzing slit upstream of said moving film.
 3. A device according to claim 1, wherein the system for detecting the intensity of the diffracted emergent beam comprises a stationary screen, a selecting slit in said screen, downstream of the crystal, said diffracted beam, passing through said slit and including a stationary photographic film a short distance behind said selecting slit. 